Electric furnace apparatus and method of operating the same



Aug. 2s, 1923.

`J. A. SEEDE ELECTRIC FURNAGE APPARATUS AND METHOD oF OPERATING THE SAME Filed May 8 1916 Inventor' Jo hn .7615 ede., bym

His aCTttorr-Ieg.

Patented ug. 28, 19235.`

UNITED STATES 'JOHN a.v enana, or scHENEcTAnY, Naw

YORK, ASSEGNSDR '0y GENEBLELECTRII@ colapsar, a conronarron or new nona.

ELECTRIC EUENCE APPARATUS AND HE'EHGJD @E GPERTING TEF SME.

Application led Hay 6, To all 'whom 'it may concern.: .Be it known that l, JOHN A. SEF/DE, a citizen of the United States, residin at Schenectady, county of Schenectady, gtate of New York, have invented certain new and usefui improvements in Electric Furnace Apparatus and Methods'of Operating the Same, of' which the following is a specication.

-When an electric arc furnace operated with alternating current is char ed with unfused iron or steel, considerable di culty sometimes is experienced, particularly in large furnaces, to get enough energy into the furnace atv starting to melt the charge. This diiiiculty is caused very largely by the magnetization of the charge and the consequent reactance introduced into the supply circuit. F or example, with .a -ton furnace sup/ plied with energy at 17,300 amperes at 100 volts, 60

. cycles, the reactance during the melting operation may beso high that it would be I .dicult' to get more than about 1,500 kilowatts into the furnace.

In accordance with my present invention, this dilculty is overcome y increasing'the length of the arc and either increasing the operating voltage or decreasing the reactivity of the circuit during the melting period when the'reactance of the charge is high. The voltage of the energy supply may be 1ncreased in any way to enable av lon er arc to be maintained, for example, by s ifting `the transformer connections. -My invention in one of its aspects comprises a furnace connected to a. transformer provided with means for varying the'operating voltage.

The accompanying drawing illustrates-f an apparatus Lfor carrydiagrammatically ing out my invention by chan ing the connections .of the primary windings of the su ply transformer.,

he drawing shows in section an arc furnace comprising a container 1, in which a is being melted, the heat belng generated by arcs between the charge and the electrodes 3, 4 and 5, Ares ectively. As indicated in the drawing, t e electrodes tend to melt shafts or holes into thecharge before the entire mass becomes molten and to become surrounded by the unfused charge. The magnetic material, therefore, is magi netized by the current and exercises a cholrirg effect on the current so that it is 25, 26 and 22 respective 1316. Serial No. 98,047.

dicult to nace to me a period operation. ln thesupply system illustrated, the electrode nected to a transformer having primary windings 8.', 9, 10, and secondary windings 11, 12, 13, vthe latter being normally fixedly connected to the electrodes as the conductors are very heavy and hence not easily rearranged by switching. In the example shown the secondary coils are shown as connected in delta but some other connection ma be used.

n electric arc furnace charged with iron or steel is operated ordinarily with an arc about one inch 'in length consuming about Volts. In order to get sufficient energy into the furnace to overcome the starting dilicultles above noted, I prefer to operate with a longer arc and a materially higher yoltage, for example, an arc abut three inches long, and consuming about 100 volts.

The increase in operating voltage ma be obtained by connectin the primary coils in delta by moving switc es 14, 15, 16 to the leftthereb connecting conductors 17, 18, to each otlier at the contacts 19, 20, conductors 21 the conductors 25, 26, at the contacts 27, 28.-. Electric energy is supplied through the conductors 29, 30,31 from a three-phase s stem'32 of suitablecurrent and voltage. 'lyhe switches mentionedA together with a switch 33 'may all be connected to a rod 34 and -moved in unison thereby..

' AW'hen the charge hasv en melted, and the long arc begins to send too much heat to the side walls and roof of the furnace, the arc may to advantage be shortened to operate with 'a voltage drop of about 60 volts. The connections are shifted tol Y, or star, by

moving the switch 34 to the right, thereby charge 2 of iron or steel scrap, or the like, f

connecting the conductors 17, 18 and 21 to a common point by the switch 33 at the con# tacts 5 and connecting the opposite ends `ofceac coil 8', 9 and 10 to the dierent phases of the supply s stem by conductors y, at the switch contacts 37, 38 and 36. This Y connection decreases the secondary volta e causin the input of a .lesser amount o energy mto the furnace.

It may sometimes be desirable to operate supply conductors 6, 7 and 8 are conand 22 at 'contacts 23, 24, andwith a short arc for a period at the very beginning of the operation, and then lengthen the arc while maintaining the current value. In this event the primary windings are connected first in Y, then when the electrodes have penetrated the charge, and have develo d asatisfactory arci'ng surface on the c arge, the transformer connections are shiftedhto delta and the arc lengthened. Finally when the charge has been largely melted, the connections are restored to Y and the arc is'shortened to thenormal length.

Other methods of increasin the voltage to increase the energy consumed in the arc to overcome the choking eii'ect on the supply current of a magnetized charge in the furnace, may be used within the scope of my invention. `For example, the reactivity of the energy supply may be decreased by decreasmgv the periodic1ty of the current, o r by changing the wave shape and thus minimizing t e energy reducing the eect of the reactance.

What I claim as new and desire to secure Letters Patent of the United States, is,- 1. The method of operating an electric arc furnace supplied with alternating current which consists in first operating the furnace with a short arc, thereupon increasing the length of arc while maintainingthecur- 'rent value, and finally 'reducing the I ength of arc to operate with a lower energy input.

2. The combination of an electric furnace, a three-phase transformer having secondary lixedly connected to the electrodes of said furnace, and means for connecting the primary windings of the transformer at will either in delta or st'ar.

3. The combination of an electric arc furnace, a polyphase transformer having secondary windings fixedly connected to the electrodes of' said furnace, and means for changing'the arrangement of the primary windings to varythe secondary vo tage of the transformer. 4. The combination of an electric arc furnace having a plurality of electrodes, a transformer, normally fixed electric connec tions between the secondary of said transformer and said electrodes, and means for changing the arrangement of the primary windings of said transformer to vary the voltage impressed on the furnace electrodes.

5. The combination of an electric arc furnace having a plurality of electrodes, transformer secondary windings normally connected lixedly to said electrodes, primay.A i windings inductively related to said secon ary windings and means for changing the arrangement of said primary windings from delta to star or star to delta. ,l

6. The combination'of an electric arc furnace having a plurality of electrodes, a set of transformer secondary coils connected to said electrodes, a set of corresponding primary transformer windings, and meansv for changing the arrangement of one of said sets of windings while maintaining the electrical connections of the other set intact.

'1n witness whereofyl have hereunto set my hand this 6th day df May, 1916.

JOHN A. SEED-E. 

